1. Field of the Invention
The present invention relates to using image-guided surgery techniques to collect data to insure accurate tracking of an ablation device.
2. Background Information
For over fifty years, diagnostic images have been used for surgical guidance, especially in the field of neurosurgery. Image-guided surgery implements two fundamental ideas: first, the concept of an image-space to physical-space mapping or registration, and second, the use of an extracranial device for accurate surgical guidance without direct visualization. Such ideas gave birth to stereotactic neurosurgery, a technique for locating targets of surgical interest within the brain relative to an external frame of reference. This is traditionally defined as the temporary attachment of a mechanical frame to the skull or scalp in order to define a 3-D frame space around a patient. With the advent of computed tomography (CT), the coordinates of a target (i.e. tumor) in image space could be assigned coordinates in frame space if the CT images were obtained with the attached frame. Unfortunately, frames are uncomfortable to patients, must be applied prior to imaging, and are cumbersome in the imaging environment and the operating room.
These factors led to the development of frameless stereotactic surgical systems, or interactive, image-guided surgery (IIGS) systems. In traditional IIGS systems, present surgical position is tracked during an operation and displayed on pre-operatively obtained tomographic images. As the surgeon changes the current surgical position, displayed images are updated in real time. In one of the earliest IIGS systems, physical space surgical position was determined using articulated arms. The position of an articulated pointer was calculated using a personal computer (PC) and overlayed on tomographic images. Magnetic resonance images (MRI) and CT negative films were scanned into the computer and displayed as images on a video interface. Other early image-guided surgical systems also used electromechanical 3-D coordinate digitizers to indicate present surgical position on various representations of patient data, including 2-D transverse, coronal and sagittal CT or MRI slices, and on image renderings of the physical object surface. Since it was necessary to have computers capable of managing large volumes of image information ( greater than 100 Mbytes) and updating the display quickly, most early IIGS systems were developed with VME bus devices running UNIX.
Early IIGS systems were developed on PCs using multiple processors. In a task-oriented asymmetric multiprocessing (TOAM) system developed in 32 bit extended DOS, discrete tasks such as physical space localization, data fetching, and display were conducted asynchronously on specialized processors which communicated with inexpensive, general purpose processors that worked as loaders and schedulers. For physical space localization, several articulated arms with six degrees of freedom were first developed. These cumbersome arm devices were eventually replaced with lightweight cylindrical pen-like probes which could be tracked more easily in the operating room using an optical triangulation system. The spatial location of the guidance instrument was determined using a collection of discrete processors which continually update the physical space location. This location was then passed to the central processor where it was mapped into image space. Once the image space map was complete, the appropriate tomographic slices were selected and displayed. Because this system was designed before the advent of large memory availability, image display relied heavily on hardware manipulation using disk controllers to load images directly from the hard drive. Control of the bus was passed from the main processor to the disk drive controller, where the correct image was fetched and sent to the display processor.
With the continuing increase in performance to price, processes which could only be performed on workstation class machines are now routinely performed on PCs. As the PC hardware evolved, however, it became apparent that DOS-based systems would not have the continuing support of hardware vendors.
Because of these considerations, a need for an operating room image-oriented navigation system (ORION) emerged. ORION was developed in Windows NT using MS Visual C++ 6.0 with the Win32 API. Not only was this system designed to be faster than the previous one, but it was not necessary to redesign the software with each hardware advance. Components of the system were developed as dynamic link libraries (DLLs), so that new technology could be incorporated into the system without a complete software rewrite. The system is also somewhat portable. It runs adequately on any PC with a 200 MHz or higher Pentium processor and 128 MB of memory which also has the appropriate video card and 3-D localizer hardware and software.
When designing an image-guided surgical system, it is critical that the precise location of an ablative instrument used to perform image-guided surgery be determined on a continuous basis (e.g., update rates approaching 30 frames per second). Further, in an effort to insure the utmost in precision, an ablation zone of the ablative instrument, the tissue being operated on, and a particular portion of the tissue to be resected or ablated during surgery must also be continuously and accurately tracked.
What is needed is a method and apparatus for collecting and processing physical space data for use while performing image-guided surgery, such that tumors and lesions in the tissue of a living patient can be accurately located, and resected or ablated with a precisely tracked ablative instrument. The present invention fulfills such a need.
In interactive, image-guided surgery, current physical space position in the operating room is displayed on various sets of medical images used for surgical navigation. The present invention is a PC-based surgical guidance system which synchronously displays surgical position on up to four image sets and updates them in real time. There are three essential components and techniques which have been developed for this system: 1) accurately tracked ablative instruments, 2) accurate registration techniques to map physical space to image space, and 3) methods and apparatus to display and update the image sets on a computer monitor. For each of these components, a set of dynamic link libraries has been developed in MS Visual C++ 6.0 supporting various hardware tools and software techniques. Surgical (i.e., ablative) instruments are tracked in physical space using an active optical tracking system. Several different registration algorithms were developed with a library of robust math kernel functions, and the accuracy of all registration techniques have been thoroughly investigated. The present invention was developed using the Win32 API for windows management and tomographic visualization, a frame grabber for live video capture, and OpenGL for visualization of surface renderings. This current implementation of the present invention can be used for several surgical procedures, including open and minimally invasive liver surgery.
In a method according to the present invention, physical space data is collected and processed for use while performing image-guided surgery. Tissue of a living patient is surgically exposed. Physical space data is then collected by probing a plurality of physical surface points of the exposed tissue, the physical space data providing three-dimensional (3-D) coordinates for each of the physical surface points. Based on the physical space data collected, point-based registrations used to indicate surgical position in both image space and physical space are determined. The registrations are used to map into image space, image data describing the physical space of an ablative instrument used to perform the image-guided surgery, an ablation zone of the instrument, the tissue, and a particular portion of the tissue to be resected or ablated. The image data is updated on a periodic basis.
The collection of physical space data may be performed by sweeping an optically tracked localization probe over the surface of the exposed tissue. The tissue may be the patient""s liver and the particular portion of tissue to be resected or ablated may be a hepatic metastatic tumor.
Prior to surgery, tissue of the patient may be scanned to acquire, store and process a 3-D description of the organ or structure of interest (e.g., a 3-D reference). A triangularized mesh may be created based on the scanned tissue. The volumetric center of a particular portion of the tissue to be resected or ablated during the surgery may be determined, wherein an algorithm using the triangularized mesh and the collected physical space data may be implemented to determine the point-based registrations. The algorithm may be a Besl and Mackay iterative closest point (ICP) registration algorithm.
The scanning of the tissue may be performed by one of a computerized tomography (CT) scanner, a magnetic resonance imaging (MRI) scanner and a positron emission tomography (PET) scanner.
The ablative instrument may emit a plurality of intermittent infrared signals used to triangulate the position of the ablative instrument in 3-D image space. The signals may be emitted from a plurality of infrared emitting diodes (IREDs) distributed over the surface of a handle of the ablative instrument in a spiraling fashion. The IREDs may flash in time sequence. Each IRED may have a 60 degree transmission angle.
The image data may be updated in real time at 30 Hz or greater. The ablative instrument may use one of radio-frequency and cryoablation to resect or ablate the particular portion of the tissue. The ablative instrument may have a tip comprising an ablation device. The ablation zone may extend 1 centimeter from the tip of the ablative instrument.
Information from the localizer may also be used in conjunction with laparoscopic or endoscopic imaging. Points from 3-D physical space may be mapped to 2-dimensional (2-D) image space. Points from 3-D physical space may be mapped to 2-dimensional (2-D) laparoscopic video space using a direct linear transformation (DLT). Points from 3-D physical space may be mapped to 3-D tomographic image space. Points from 3-D physical space may be mapped to 2-dimensional (2-D) endoscopic image space.
In an apparatus according to the present invention, physical space data is collected and processed for use while performing image-guided surgery. The apparatus comprises a probe instrument, an ablative instrument and an image data processor. The probe instrument collects physical space data by probing a plurality of physical surface points of surgically exposed tissue of a living patient. The physical space data provides three-dimensional (3-D) coordinates for each of the physical surface points. The ablative instrument may resect or ablate a particular portion of the exposed tissue.
The image data processor comprises a computer-readable medium holding computer-executable instructions which, based on the physical space data collected by the probe instrument, determine point-based registrations used to indicate surgical position in both image space and physical space. Using the point-based registrations to map into image space, image data describing the physical space of an ablative instrument used to perform the image-guided surgery, an ablation zone of the ablative instrument, the tissue, and a particular portion of the tissue to be resected or ablated. The image data is updated on a periodic basis.
The probe instrument may be swept over the surface of the exposed tissue. The apparatus may also comprise a scanning device for scanning tissue of the patient to acquire, store and process a 3-D reference of tissue prior to the tissue being surgically exposed. The image data processor creates a triangularized mesh based on the scanned tissue, determines the volumetric center of a particular portion of the tissue to be resected or ablated during the surgery, and implements an algorithm using the triangularized mesh and the physical space data collected by the probe instrument to determine the point-based registrations. The algorithm is a Besl and Mackay iterative closest point (ICP) registration algorithm.
The scanning device may be one of the following scanners: a computerized tomography (CT) scanner, a magnetic resonance imaging (MRI) scanner and a positron emission tomography (PET) scanner.
The ablative instrument may emit a plurality of intermittent infrared signals used to triangulate the position of the ablative instrument in 3-D image space, the signals being emitted from a plurality of infrared emitting diodes (IREDs) distributed over the surface of a handle of the ablative instrument in a spiraling fashion. The IREDs may flash in time sequence. Each IRED may have a 60 degree transmission angle. The image data may be updated in real time at 30 Hz or greater.
The ablative instrument may use one of radio-frequency and cryoablation to resect or ablate the particular portion of the tissue. The ablative instrument may have a tip comprising an ablation device. The ablation zone may extend 1 centimeter from the tip of the ablative instrument.
Points from 3-D physical space may be mapped to 2-dimensional (2-D) image space. Points from 3-D physical space may be mapped to 2-dimensional (2-D) laparoscopic video space using a direct linear transformation (DLT). Points from 3-D physical space may be mapped to 3-D tomographic image space. Points from 3-D physical space may be mapped to 2-dimensional (2-D) endoscopic image space.